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Fix latent portability issue in pgwin32_dispatch_queued_signals().

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The first iteration of the signal-checking loop would compute sigmask(0)
which expands to 1<<(-1) which is undefined behavior according to the
C standard.  The lack of field reports of trouble suggest that it
evaluates to 0 on all existing Windows compilers, but that's hardly
something to rely on.  Since signal 0 isn't a queueable signal anyway,
we can just make the loop iterate from 1 instead, and save a few cycles
as well as avoiding the undefined behavior.

In passing, avoid evaluating the volatile expression UNBLOCKED_SIGNAL_QUEUE
twice in a row; there's no reason to waste cycles like that.

Noted by Aleksander Alekseev, though this isn't his proposed fix.
Back-patch to all supported branches.
This commit is contained in:
Tom Lane 2016-04-04 11:13:17 -04:00
parent eb7308d298
commit 58666ed28a
1 changed files with 5 additions and 4 deletions
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9
src/backend/port/win32/signal.c
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@ -33,6 +33,7 @@ HANDLE pgwin32_initial_signal_pipe = INVALID_HANDLE_VALUE;
*/
static CRITICAL_SECTION pg_signal_crit_sec;
/* Note that array elements 0 are unused since they correspond to signal 0 */
static pqsigfunc pg_signal_array[PG_SIGNAL_COUNT];
static pqsigfunc pg_signal_defaults[PG_SIGNAL_COUNT];
@ -105,15 +106,15 @@ pgwin32_signal_initialize(void)
void
pgwin32_dispatch_queued_signals(void)
{
int i;
int exec_mask;
EnterCriticalSection(&pg_signal_crit_sec);
while (UNBLOCKED_SIGNAL_QUEUE())
while ((exec_mask = UNBLOCKED_SIGNAL_QUEUE()) != 0)
{
/* One or more unblocked signals queued for execution */
int exec_mask = UNBLOCKED_SIGNAL_QUEUE();
int i;
for (i = 0; i < PG_SIGNAL_COUNT; i++)
for (i = 1; i < PG_SIGNAL_COUNT; i++)
{
if (exec_mask & sigmask(i))
{